​Four groups of students (A – D) were asked to determine whether memory B cells generated in mice immunized with ovalbumin (OVA), in Complete Freund’s adjuvant (CFA), could mount a secondary antibody response (recall response) to OVA in vitro. The groups did the following experiments:

• Group A students harvested serum from the mice, loaded it on OVA-coated ELISA plates, and showed that IgG and IgA anti-OVA antibodies were present.
• Group B students harvested long-lived plasma cells from the bone marrow of the mice, plated them in culture for 5 days, and showed anti-OVA antibodies in the supernatant by ELISA.
• Group C students infected an epithelial cell line with the virus and showed that spleen cells from the mice could kill the infected targets.
• Group D students stimulated spleen cells from the mouse with OVA for 5 days and showed anti-OVA antibodies in the supernatant by ELISA.

Correct option is D

​The question asks which group correctly tested for the ability of memory B cells to mount a secondary antibody response in vitro. Let's analyze each group's experiment:

• Group A: Incorrect

  • Measured IgG and IgA antibodies in the serum of immunized mice.
  • This only confirms the presence of circulating antibodies but does not test the recall response (secondary response) of memory B cells.
    

• Group B: Incorrect

  • Harvested long-lived plasma cells from the bone marrow and tested for antibodies.
  • Plasma cells continuously secrete antibodies but do not represent memory B cell activation or secondary response.
    

• Group C: Incorrect

  • Used spleen cells to test for cytotoxic activity against infected cells.
  • This experiment focuses on T-cell-mediated cytotoxicity, not memory B cells or antibody recall response.
    

• Group D:  Correct

  • Stimulated spleen cells with OVA for 5 days and measured antibody production.
  • Memory B cells reside in the spleen and require antigen stimulation to differentiate into plasma cells, which then produce antibodies.
  • This correctly assesses the recall response of memory B cells.
    

Thus, the correct answer is Group D (Option 4).

Information Booster

1. Memory B Cells Function: These cells are generated after primary immune responses and can rapidly differentiate into plasma cells upon re-exposure to an antigen.
2. Secondary Response: Memory B cells mount a faster and stronger antibody response compared to naïve B cells.
3. Spleen as a Site of Memory B Cells: The spleen contains a reservoir of memory B cells, which can be reactivated upon antigen exposure.
4. Plasma Cells vs. Memory B Cells: Plasma cells continuously secrete antibodies, while memory B cells require stimulation to differentiate into antibody-producing cells.
5. ELISA in Immune Response Studies: ELISA is widely used to detect antibodies in culture supernatants, confirming the activation of B cells.
6. Antigen Restimulation: To test memory B cell function, scientists often reintroduce the antigen and measure the response.
7. Time Frame of Activation: Memory B cells differentiate into plasma cells within days, as seen in Group D's experiment.